1. Field of the Invention
The present invention is directed to a method and apparatus for casting conductive and semi-conductive materials, and more particularly, to a method and apparatus for casting such materials in a substantially continuous manner with minimal contamination of the cast material.
2. Description of the Prior Art
It is known that conductive and semiconductive materials can be cast into ingots having specific cross-sectional shapes. To date, processes for casting such materials have employed batch casting techniques wherein a predetermined amount of feed material, in either a solid or molten state, is introduced into a casting mold having a specific cross-sectional shape. If the feed material is introduced into the mold in a solid state, a means for melting the material is provided. Once the feed material is in a molten state, the material is allowed to solidify and cool within the mold to produce a cast ingot having a desired cross-sectional shape, as determined by the configuration of the inner walls of the mold.
Such batch casting processes suffer from at least two common drawbacks. First, since the cast ingots are produced on a batch-by-batch basis, the overall production of ingots is limited by the number of casting molds available for use at any one time, and is further limited by the lengthy production time which is required for the melting, solidification and cooling of each batch. Second, in all known batch processes, the feed material is allowed to contact the inner walls of the casting mold during the melting and/or solidification stages. When the production of a high purity ingot is desired, such contact is detrimental since contaminants from the inner walls of the mold are introduced into the molten material and become entrapped in the crystalline structure of the resultant ingot. In addition, when an ingot having large crystalline grain sizes is desired, contact between the molten material and inner walls of the mold during solidification is detrimental due to the effects of wall nucleation.